Question

A truck with a heavy load drove from Boston to New York at 45 mph. After unloading, it returned from New York to Boston at a speed of 65 mph. What was its average speed for the whole trip?

Answer 1

average speed = 53.1818181818

Explanation:

The journey from Boston to New York and New York to Boston covers the same distance. Therefore let the distance be x.

Boston to New York

speed = distance / time

45 = x/time

time = x/45

New York to Boston

speed = distance / time

time = x/65

total time for the journey = x/45 + x/65 = (13x + 9x)/585 = 22x/585

total distance = 2x

average speed = total distance/total time

average speed = 2x × 585/22x

average speed = 585/11

average speed = 53.1818181818